Extreme pressure belted structures and assembly method therefor

ABSTRACT

A die (40) for extrusion of optical grade fibers has its hard insert (42) placed under compression within a sleeve (44). Sleeve (44) is provided with a tapered interior surface (50) which matches the tapered exterior surface (48) of the insert (42). A metal lubricating layer (60) is provided between the tapered surfaces. The insert is pressed in to obtain compressive prestressing thereof, and the lubricating metal diffuses at the tapered surfaces to lock the insert in the sleeve.

This is a continuation of application Ser. No. 06/302,891 filed Sept.16, 1981, now abandoned, in turn a division of application Ser. No.06/137,092 filed Apr. 4, 1980, now U.S. Pat. No. 4,308,044 which waspatented Dec. 29, 1981.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for assembly of high pressurevessels.

2. Description of the Prior Art and Background Considerations

The fabrication of containers for extreme pressures was originated anddeveloped by P. W. Bridgman where concentric prestressed belts of highstrength alloys are assembled about a container wall to place theinnermost layer thereof under compression. Conventionally, prestressingis achieved by heating and expanding the outer belts with respect to theinner layers of the container. Upon assembly and cooling, the beltscontract upon the inner layers. Such thermal expansion is limited tosmall dimensional changes, and does not easily generate largedimensional changes, e.g., approximately one percent. In addition, evenif sufficient expansion were obtainable by thermal means, the requiredhigh temperatures would change the mechanical properties of thecomponents. Therefore, it has been necessary to look to other means bywhich the necessary pre-stress can be obtained.

In the fabrication of certain types of optical fibers, extrusion at highpressure is employed. The cylinder surrounding the extrusion piston usedin this application must be of great strength and be capable ofcontaining the very high pressures developed during extrusion. In thepresent invention, sintered carbides, such as tungsten or titanium, werefound suitable for the extrusion cylinder. These materials have thenecessary strength and have no chemical or physical effect on theextruded fiber. However, these high strength materials are also brittleand have a tendency to crack under tension. Therefore, it is necessaryto fashion the sintered carbide as a tubular insert and to enclose itunder great compressive pre-stress within a sleeve of hardened tool ortempered alloy steel so that, even during the application of the highextrusion pressures therein, there would still be some remainingcompressive force exerted upon the carbide insert. To assemble theinsert in the sleeve for the reasons described above, thermal expansionand contraction was insufficient to generate the required largedimensional changes of about one percent. Also, as stated above, anyheating necessary to obtain a thermal expansion would destroy the temperof the components.

Therefore, the titanium carbide die was inserted into the hardened toolsteel sleeve first by concentrically tapering the mating surfaces of theinsert and the sleeve with a slight oversizing of the insert withrespect to the sleeve, and then by axially compressing the insert intothe sleeve. Such a method of assembly, however, gave rise to a dual,contradictory problem in that low friction during assembly, and highfriction after assembly for retention of the insert within the sleevewere required. For example, a titanium carbide insert lubricated with ahigh pressure lubricant and retained in a sleeve, was expelled withexplosive force after release of the assembly pressure, even though thetaper angle of the mating surfaces was only 1.2°. Yet, if no lubricantwere used, the assembly process would have caused galling, resulting ina scored interface between the insert and the sleeve with unknown andundesired mechanical properties.

SUMMARY OF THE INVENTION

Resolution of these and other problems was obtained by the presentinvention by providing lubrication of the tapered surfaces duringassembly, and locking of the assembly after its completion by mechanicaland metallurgical techniques.

Mechanically, mateable grooves are formed in the cooperating taperedsurfaces of the insert in the sleeve. In the preferred embodiment, aradially compressible ring is installed in the external cylinder insertgroove. During axial compression with lubrication, the ring does notproject above the adjacent surface but is squeezed into its groove untiltotal insertion is completed. As soon as the tapered insert reaches itsdesired penetration within the sleeve, the ring expands and snaps intothe juxtaposed groove and firmly and permanently locks the assemblytogether.

Alternately, a radially expandable ring may be retained in the internalgroove of the sleeve; however, in this case, a special pilot pin must beinserted into the sleeve to permit expansion of the ring, and assemblyof the insert.

Metallurgical locking is obtained by coating the insert and/or thesleeve with a metal which is capable of lubricating the interface duringassembly and which will subsequently diffuse into the surrounding metalsof the insert and the sleeve to lock them together. Typical metalsinclude gold, copper, silver, nickel and aluminum.

It is, therefore, an object of the present invention to provide for alow friction assembly and permanent bond of concentric taper belted highpressure containers.

Another object of the present invention is to provide for assembly ofultra-high pressure vessels without use of thermal expansion techniques.

Other aims and objects as well as a more complete understanding of thepresent invention will appear from the following explanation ofexemplary embodiments and the accompanying drawings thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a first embodiment of the present invention illustratinga mechanical locking technique, with the taper of, and the spacingbetween, component parts being greatly exaggerated;

FIG. 2 is an enlarged view of a mechanical interlocking of FIG. 1; and

FIG. 3 illustrates the metallurgical technique of interlocking thecomponents, again shown with great exaggeration of the taper of andspacing between the parts.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, an assembly 10, useful, for example, inextrusion of optical fibers, comprises a cylinder or insert 12 held andlocked within a sleeve 14. The cylinder is provided with a bore 16through which the fiber materials are pushed for extrusion. Exemplarycylinder materials comprise tungsten or titanium carbide which areplaced under precompression by being oversized with respect to thesleeve. To maintain the proper compressive forces on insert 12, sleeve14 may be formed of a hardened tool or tempered alloy steel.

In order to form the assembly, insert 12 and sleeve 14 are formedrespectively with exterior and internal tapered surfaces 18 and 20, witha taper decreasing from the top 22 of the assembly to its bottom 24. Anexemplary taper angle may be 1.2°.

Assembly is effected by positioning insert 12 at top surface 22 andaxially forcing the insert along internal surface 20 with a hydraulicpress until the tops of the insert and the sleeve are nearly flush witheach other. To insure that the two components remain interlocked,grooves 26 and 28 are formed respectively externally on the cylinderinsert and internally in the sleeve are positioned to face one anotherwhen the insert and the sleeve are completely assembled together. Asplit ring 30 effects the interlock. The ring is originally compressedso that it will reside within groove 26 in its compressed state withoutprojecting beyond the external surface of the tapered insert. The onlycondition of compression is that the ring's outer surface 32 slidewithin internal surface 20 of the sleeve.

For assembly, the ring is either compressed into external groove 26 oncarbide insert 12 or expanded into internal groove 28 in the sleeve anda lubricant placed on surfaces 18 and 20. The tapered insert is axiallyintroduced into the sleeve and, after it has reached the desiredpenetration within sleeve 14, ring 30 expands or contracts into itsjuxtaposed groove to firmly and permanently interlock the assembly.

Metallurgical locking is illustrated with respect to FIG. 3 in whichassembly 40 includes an insert 42 and sleeve 44, which are similarlyconfigured as the sleeve and insert of FIGS. 1 and 2. In a like manner,insert 42 is provided with an external tapered surface 48 and sleeve 44is provided with an internal tapered surface 50. The interlocking mediumhere, however, comprises a metal 60 which is placed on one or both ofsurfaces 48 and 50. The metal must also be capable of acting as alubricant. Examples include gold, copper, silver, nickel and aluminum.In one experiment, a layer of gold 5 micrometers thick was placed on aninsert of titanium carbide. Insert 42 was placed in position to beaxially driven within sleeve 44. Metal 60 of gold provided the necessarylubrication and, after completion of the two component assembly, thegold diffused into the insert and the sleeve to form a metallurgicaldiffusion bond therebetween at their surfaces 48 and 50.

Although the invention has been described with reference to particularembodiments thereof, it should be realized that various changes andmodifications may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method for assembling a prestressed extrusiondie, comprising the steps of:providing a sleeve having an openingdefined by a tapered inner surface; providing an insert comprisingmaterial which is weak in tension and having a tapered outer surface andan inner extrusion bore, in which the outer surface is sized withrespect to the inner surface so that, when the insert is placed withinthe sleeve, the inner and outer surfaces are adjacent each other and theinsert will be placed under compression by the sleeve; coating matterhaving lubricating and bonding characteristics on at least one of thetapered surfaces; pressing the insert into and within the sleeve aidedby the matter's lubricating characteristic to prestress the insert; andbonding the insert and the sleeve together by use of the matter'sbonding characteristic.
 2. A method for assembling a prestressed beltedstructure useful as an extrusion due, comprising the steps of:providinga metallic sleeve having an opening defined by a tapered inner surface;providing a metal insert having a tapered outer surface and a throughextrusion bore, in which the outer surface is sized with respect to theinner surface so that, when the insert is placed within the sleeve, thesurfaces are adjacent each other and the insert is compressed by thesleeve; coating a lubricant metal on at least one of the taperedsurfaces in which the lubricant metal comprises one of gold, copper,silver, nickel and aluminum; assembling the insert and the sleeve sothat the surfaces are concentric and are separated substantially only bythe metallic lubricant by pressing the insert into the sleeve with theaid of the lubricant metal, thereby to (compress) the insert; andlocking the insert and the sleeve together by diffusing the metallubricant into the insert and the sleeve at their surfaces forpreventing slippage therebetween.
 3. A method according to claim 2 inwhich the lubricant metal comprises an approximately 5 micrometer layerof gold, the insert comprises tungsten carbide, and the sleeve comprisestempered alloy steel.
 4. A method according to claim 2 in which thesurfaces are concentric and the taper of the tapered surfaces in thesleeve and on the insert is substantially 1.2° to the longitudinal axesthereof.
 5. A method according to claim 2 in which the tapered surfacesin the sleeve and on the insert have a substantially 1.2° taper alongtheir longitudinal axes.
 6. A method for assembling a prestressed beltedstructure useful as an optical fiber extrusion die, comprising the stepsof:providing a metallic sleeve having an opening defined by a (taperedinner surface); providing a metal containing insert having a taperedouter surface, the outer surface being sized with respect to the innersurface so that, when the insert is placed within the sleeve, the innerand outer surfaces are adjacent each other; providing a through bore inthe insert for the use of the prestressed structure as a die forextruding optical fibers; coating a metallic lubricant on at least oneof the tapered surfaces; pressing the insert into and within the sleeveto compressively prestress the insert; and locking the insert and thesleeve together by permitting diffusion of the metallic lubricant intothe insert and the sleeve for preventing slippage therebetween.
 7. Amethod for assembling a prestressed extrusion die comprising the stepsof:providing a sleeve having an opening therein defined by a taperedinner surface having a taper angle of substantially 1.2° along itslongitudinal axis; providing a brittle insert with an extrusion boretherein in which the insert has an outer surface sized to the opening inthe sleeve so that the insert can be inserted into the sleeve undercompression, with the outer surface being tapered at substantially thesame angle as the opening in the sleeve; lubricating at least one of thetapered surfaces by coating a lubricant thereon having also thecapability of bonding the surfaces together; inserting the insert intothe sleeve so that the tapered surfaces contact with the lubricantinbetween and so that the sleeve compresses the insert; and bonding theinsert and the sleeve together by the lubricant for preventing slippagetherebetween.